The prospect of a human baby with three biological parents has moved closer after scientists created monkeys using a technique that one day could stop children from inheriting severe genetic diseases.

The birth of four healthy macaque monkeys in the US offers the strongest evidence yet that DNA can be transplanted safely from one egg to another to correct genetic defects that damage health.

The successful experiment in a close human relative suggests that it should be possible within a few years to use the method to help women who carry genetic disorders to avoid passing them to their children.

It should allow scientists to replace faulty “cellular batteries” called mitochondria, which affect about 1 in 6,500 births. While most mitochondria defects have mild effects, some can trigger severe brain, heart, muscle and liver conditions, as well as cancer, diabetes, blindness and deafness.

The technique is controversial, however, because the children it creates would inherit genetic material from three parents. The mother and father would contribute most of their child’s DNA but a small amount would come from a second woman donating healthy mitochondria.

Such children would be the first produced by germline genetic engineering, in which genes introduced by artificial means would be passed to successive generations.

Shoukhrat Mitalipov, of the Oregon National Primate Research Centre, who led the research, said that this would be justified because it was the only viable approach.

“The only way to treat these defects is to replace the genes,” he said. “This is gene transfer involving the germline, which is a concern, but we are pursuing it not for general use but for patients with mutations they will pass to the next generation. We believe this technology will prevent that.”

Although more than 99 per cent of a cell’s DNA is carried in the nucleus, a small amount resides in the mitochondria — tiny energy-producing structures inherited from the mother — and it is mutations in this mitochondrial DNA that can cause disease.

In the research, published in the journal Nature, the modified eggs containing chromosomes from one female monkey and mitochondria from another, were fertilised by injecting a sperm. The resulting embryos were transferred to the wombs of surrogate mothers.

The first monkeys to be born were twins called Mito and Tracker, after a dye called MitoTracker used in the experiments. Two more monkeys were born after later experiments, named Spindler and Spindly after a genetic structure called the spindle along which chromosomes divide.

Tests showed that none of the monkeys had any trace of mitochondrial DNA from the mother that provided their nuclear DNA, suggesting that the process was successful. “We consider it a big achievement,” Dr Mitalipov said. “Anything we study and achieve in non-human primates can be translated much more easily to humans.”

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